The topic of the present study is the accumulation of new information regarding the structural modification of the DNA helix assoicated with carcinogen interactions. A few model systems have been established to analyze the conformational change of DNA resulting from covalent and non-covalent binding of carcinogenic drugs, dehydration by organic solvents, polyamines, and mutagenic amino acid pyrolysates. Stereospecificity of carcinogen interaction depends in part on the conformation of the DNA helix. Alteration of target sites of DNA structural components associated with covalent interaction with carcinogens are studied under a variety of physico-chemical experimental conditions.